Swap two integers without using a third variable

Question

I have an assignment in which I need to swap two integers without using third variable. I'm not sure how to do this. How would I code this?

Answer 1

Yes, it's possible:

Dim var1 = 1
Dim var2 = 2
var1 = var1 + var2
var2 = var1 - var2
var1 = var1 - var2

But why do you need it? The code becomes abstruse.

Answer 2

theoretically 3 ways

a = 4 , b = 5

1. Using XOR

a = a XOR b = 4 XOR 5 = 9     
b = a XOR b = 9 XOR 5 = 4
a = a XOR b = 9 XOR 4 = 5

2. Using +,-

a = a+b = 4+5 = 9     // should not overflow
b = a-b = 9-5 = 4
a = a-b = 9-4 = 5

3. Using *,/

a = a*b = 4*5 = 20    // should not overflow
b = a/b = 20/5 = 4    // should not overflow and should not be irrational number
a = a/b = 20/4 = 5    // should not overflow and should not be irrational number